Multiple tube air heating furnace



ug. 23, W4. M. H. KUHNER 479,940

MULTIPLE TUBE AIR HEATING FURNACE Filed Sept. 28, 1944 5 Shebs-Shee l MAX H. KUH/VE/ Aug. 23, w49.. M, H @HNE-R 2,479,90

MULTIPLE TUBE AlR HEATING FURNACE Filed sept. 28, 1944 s sheets-sheet 2 l www MAX H. /GUHNER Aug. 23, E949. M. H. KUHNER MULTIPLE TUBE AIR HEATING FURNACE 3 Sheets-Sheet 5 Filed Sept. 28, 1944 OOOODOQDOOOOO 0000000000000 Patented Aug. 23, 1949 MULTIPLE TUBE AIR HEATING FURNACE Max H. Kuhner, Worcester, Mass., assigner to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application September 28, 1944, Serial No. 55.6,256

5 Claims.

This invention relates to heating furnaces, and more particularly to furnaces for heating gases, such as air, to relatively high temperatures for use in drying or other industrial processes.

It is one object of the inventnon to provide a gas heating furnace of relatively simple and inexpensive construction which will be capable of operating efficiently throughout a long life of useful service.

It is a further object of the invention to provide a gas heating furnace utilizing the heat oi burning fuel and arranged to avoid any contamination of the gas by the gaseous products of combustion.

It is a further object of the invention to provide a gas heating furnace so arranged that the various parts thereof will be adequately protected against overheating.

With these and other objects in View, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specication and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention, and in which like 1 reference numerals indicate like parts,

Fig. l is a longitudinal section through a gas heating furnace, taken on the line I-I of Fig. 2; Fig. 2 is a section taken on the line 2-2 of Fig. i;

Fig. 3 is a section taken on the line 3--3 of Fig. l;

Fig. 4 is a section taken on the line 4--4 of Fig. 1; and

Fig. 5 is an enlarged sectional view illustrating the application of refractory material to a tube sheet.

The embodiment illustrated comprises a furnace combustion chamber IU having a iront wall Ei, a rear wall I2, opposed side walls I4, a floor l5, and a roof i6, all constructed of suitable refractory material. A burner I8 serves to discharge fuel and air rearwardly through an opening iii in the front wall I I7 for combustion in the chamber I0. Pulverized fuel is supplied to the burner I8 through a pipe 28 by means of a pulverizer 22 having an adjustable feeder 23. The floor i5 slopes downwardly toward the front at a slight angle. Access to the combustion chamber l may be had through doors 24 in the front wall tl and doors 25 in the rear wall I2. These doors 24 and 25 are located immediately above the floor l and they can be used for the removal of ashes which accumulate on the floor. The roof I6 is in the form of a suspended flat arch of well known construction having suitable supporting metal beams 21. The rear edge of this arch I6 terminates somewhat in front of the rear wall I2 to provide a relatively narrow transverse slot 28 forming an upwardly directed outlet opening for the escape of the gaseous products of combustion from the chamber I0.

Above the combustion chamber Il] there is provided a horizontal longitudinally extending passage 30 through which the gas to be heated flows in a rearward direction. In the illustrated embodiment this gas is air, and it is supplied under pressure to the front end of the passage by a suitable fan 3| through a connecting duct 32. The passage 30 is formed of gas-tight metal walls, the top and bottom walls being parallel and the side Walls diverging gradually in the rearward direction to provide an increasing crosssectional area which will accommodate the increasing volume of the air as it is heated. The rate of air flow can be controlled by a manually adjustable louver damper 34 at the rear end of the passage. Preferably the fan 3I supplies air not only to the passage 30 but also to the burner I8 for combustion of the fuel. For this purpose the duct 32 is connected to the burner by means of a duct 35 provided with a damper 36.

During its rearward flow through the passage 30, the air is subjected to the heating effect of the gaseous products of combustion discharged through the outlet 28 of the furnace chamber I il. This heating is brought about by passing the hot gases through vertical metal tubes mounted in the passage with their ends extending through the top and bottom walls thereof. As illustrated, there are three groups 38, 39 and 40 of these tubes providing three passes for the hot gases. The tube group 38 is located in the rear portion of the passage 30, the tube group 39 is located in front of the tubes 38, and the tube group 4i] is located in front of the tubes 3S. The gases are conducted upwardly from the furnace outlet 28 to the lower ends of the tubes 38 by a vertical passage or conduit 4I or upwardly expending cross-sectional area constructed with walls 42 of refractory material. The upper ends of the tubes 38 are connected to the upper ends of the tubes 39 by a passage 43 formed by a casing 44. The lower ends of the tubes 39 are connected to the lower ends of the tubes 48 by a passage 46 formed by a hopper 4l in which ash particles may be deposited from the gases. The upper ends of the tubes are connected te a duct 48 provided with a damper 49 and leading to a stack or induced draft fan (not shown).

Each group of tubes 38, 39 and 40 includes two separate banks which are spaced apart longitudinally of the passage 38, and the tubes in each bank are arranged in a staggered formation. There are fewer tubes in the group 39 than in the group 38, and still fewer tubes in the group 40 than in the group 39. Thus the cross-sectional area available for the flow of the heating gases is reduced Vprogressively to correspond with the shrinkage in the volume of these gases resulting from the cooling thereof. The tubes in the group 38, which are subjected to the highest gas temperature, are preferably constructed of a suitable heat-resisting metal or metal alloy.

rIhe top and bottom walls of the air passage 38 serve as tube sheets and must be relatively thick to afford the requisite strength. It is therefore desirable to protect these sheets from contact with the high temperature gases. For this purpose a layer of a suitable refractory material may be applied to the-cutersurfaces of the sheets. As best shown in Fig. 5, .the tubes may be extended beyond the sheets and flared outwardly. The refractory :material .5| may .be applied in plastic for-m, and during this application the tubes may be closed at their ends by tapered wooden plugs 52. In this way tapered openings are provided for Ythe entra-nce and exit of the gases, thereby reducing vthe draft loss through the apparatus. of the tubes serve to anchor the refractory material firmly to the tube sheets. The tube sheets will ordinarily not require this refractory protection beyond the second gas pass.

The suspended arch I6, its supporting structure 21, the walls 42, and the hopper 41 are preferably cooled by a continuous circulation of air, which will vgreatly prolong their life. For this purpose these parts are enclosed by a casing 54 which is open to the atmosphere adjacent the front end of the arc IB and behind lthe rear wall l2. A horizon-tal baffle kpla-te 55 is mounted within the casing somewhat above the beams 21 to direct the air in a desired manner. Two ducts 58 .connect the interior of the casing, above the baffle 55, with the inlets of the fan 3|, so that the fan will draw `air through the casing and bring about the'desired cooling effect.

The pulverized fuel vdischarged into the furnace chamber vIl! bythe burner |8 is combined with air supplied through the `duct 35, and this air is delivered in sufficient quantities in proportion to the rate of fuel supply'to prevent excessive combustion temperatures which would shorten the life of the furnace walls. However, too much air `at the burner would render it difrlcult `to maintain ignition yof the fuel, and for this reason I preferably limit this air flow to avoid too great a drop in the flame temperature. Consequently, furnace .gases are produced at a temperature which would be unsafe for the metal tubes 38, even though they are made of special heat-resisting alloy.

In order to protect the tubes 38 from overheating, additional air is supplied to the upper portion of the'combustion Achamber I8 for mixing with the'hot gases as they travel upwardly through the outlet opening 28. For this purpose openings 60 are provided `in the upper portion of the rear wall I2 beneath the outlet 28, and openings 6| are provided in the upper lportion of the front wall beneath the .arch I6. These air openings are provided with suitable dampers 62. The pressure within theffurnace is preferably maintained 'at a value somewhat below atmos- Furthermore the tapered ends throughthe openings 68 and 6|,

pheric pressure, so that air will be drawn inwardly through the openings 68 and 6|, and this furnace pressure is preferably held substantially constant by an automatic regulator 64 which is connected to the combustion chamber Ill' by a pipe 65. Suitable wires 66 extend from the regulator 64 to a motor 68 which is connected to the damper 49 by a linkage 69. By this means the damper 49 is regulated to maintain the desired subatmospheric pressure within the combustion chamber, so that air will enter this chamber under the control of the dampers 62. The air which enters through the front openings 6| will now vrearwardly along the lower surface of the arch I6 and thereby cool this arch and greatly prolong its life.

The admission of the air through the openings 68 and 6| is preferably controlled in accordance with the temperature of the mixed gases flowing upwardly through the passage 4| to the tubes 38. For this purpose a temperature-responsive element in the form of a thermo-couple 1i extends into the passage 4|, this element actuating a regulator or relay 12 which is connected 1 by wires 13 to a motor 15, this Vmotor being connected to the dampers 62 by a linkage 16. Even a slight increase in the temperature of the gases vin the passage 4| will be detected by the thermocouple il, and the dampers 62 will be opened tc admit more air as required to restore the desired temperature.

The rate of fuel-firing is preferably controlled to maintain a .desired predetermined temperature for the heated air discharged from the passage As shown, a temperature-responsive element in the form of a thermo-couple 89 extends into the rear portion of the passage 39, this element actuating a regulator or relay 8| which is connected by wires 82 to a motor 84. This motor is connected to the pulverizer feeder 23 by a linkage 85 and to the damper 36 by a linkage 86. Any change in the temperature of the air leaving the passage 38 will be detected by the thermo-couple 88, and the supply of fuel and air to the burner |8 will be adjusted immediately as required to restore the desired temperature.

In the ,operation of the apparatus, combustion `is maintained in the furnace 4Ill by the introduction .of air and pulverized fuel through the burner i9, and as the gaseous products of combustion travel upwardly through the outlet 28 they are mixed with air which enters the furnace through the openings 8D and 6 l.. The mixed gases are reduced in velocity by the effect of the expanding passage 4| and lthen they travel successively through the tubes .38, passage 43, tubes 39, passage 46, tubes 40, and passage 49. The fan 3| causes air to .enter the casing 54 at both the front and rear thereof, this air serving to cool the passage 42, the hopper 41, the arch I6, and the arch supporting beams '21. From the casing 54 the air flows forwardly through the ducts 56 to the fan, and thence through the duct 32 to the passage 38 and into contact with thetubes 48, 39, and 38 successively, whereby the air is heated to a desired temperature. This temperature will be held substantially constant through the action of the thermo-couple 88 and relay 8l, which 'will control the rate of supply of fuel and air to the burner |8. The regulator 64 will control the damper-49 to maintain a substantially constant predetermined sub-atmospheric pressure in the combustion chamber I8, so that air may be drawn 'into this chamber The thermocouple 'H and relay l2 will control the dampers 62 to regulate this air admission and maintain the mixture of gases in the passage 4l at a substantially constant temperature, thereby preventing overheating of the tubes 38.

The apparatus is relatively simple and inexpensive, and capable of eicient operation over long periods without repairs. Since the hot gases are separated from the air in the passage 3D by the walls of the metal tubes 38, 39 and 40, there will be no contamination of this air by the gases. The sectional construction of the air passage makes it possible to withdraw and replace individual sections in a lateral direction without disturbing adjacent sections, thereby facilitating any repairs which may become necessary.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A heating furnace comprising walls forming a chamber for the combustion of fuel and the production of hot gases, the chamber having an outlet opening for the escape of the hot gases therefrom, walls forming a passage for air to be heated, a fan to force air along the passage, the fan having an air inlet, metal tubes extending through the passage, a conduit connecting the outlet opening with the tubes, a casing enclosing the conduit in spaced relation thereto and provided with an opening to the atmosphere, and means connecting the interior of the casing with the inlet of the fan in order that the fan may draw air through the casing in cooling relation to the conduit.

2. A heating furnace comprising walls forming a chamber for the combustion of fuel and the production of hot gases, the chamber having a roof and an outlet opening for the escape of hot gases from the chamber, walls forming a passage for air to be heated, a fan connected to the passage to force air along the same, the fan having an air inlet, metal tubes extending through the passage, a conduit connecting the outlet opening with the tubes, an air supply duct connected to the air inlet of the fan, and walls located above the roof and cooperating therewith to provide a passage connecting the atmosphere with the air supply duct, the roof forming one wall of the last-mentioned passage so that the air flowing therethrough on its way to the fan will cool the upper surface of the roof.

3. A heating furnace comprising walls forming a chamber for the combustion of fuel and the production of hot gases, the chamber having a substantially :dat roof and an upwardly directed outlet opening for the escape of the hot gases,

walls forming a passage for gas to be heated, metal tubes extending through the passage, and a conduit connecting the outlet opening with the tubes, one wall of the chamber having an inlet opening therein through which air Will enter the furnace, the inlet opening being located remote from the outlet opening and in the upper portion of the chamber so that the air will iiow along the lower surface of the roof to the said outlet opening and enter the conduit with the hot gases.

4. A heating furnace having upright walls and a substantially flat roof forming a chamber for the combustion of fuel and the production of hot gases, the roof having a narrow transverse slot therethrough adjacent the rear wall to provide an outlet for the hot gases, walls forming a passage for gas to be heated, metal tubes extending through the passage, and a conduit connecting the slot with the tubes, the front wall of the chamber having openings in its upper portion through which air is admitted to flow rearwardly along the lower surface of the roof to the slot and enter the -conduit with the hot gases.

5. A heating furnace comprising walls forming a chamber for the combustion of fuel and the production of hot gases and having an upwardly directed outlet opening for the escape of the hot gases, walls forming a substantially horizontal passage above the chamber for gas to be heated, the passage walls including upper and lower walls of metal, upright metal tubes extending through the passage with their lower ends projecting below the said lower wall and ared outwardly, refractory material covering the lower surface of the lower wall and held in place by the flared ends of the tubes, and a conduit connecting the outlet opening with the lower ends of the tubes.

MAX H. KUHNER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 366,657 Evans July 19, 1887 601,590 Rossmann Mar. 29, 1898 1,151,611 Pratt Aug. 31, 1915 1,319,654 Lee Oct. 21, 1919 1,388,583 Lee Aug. 23, 1921 1,389,408 Wilputte Aug. 30, 1921 1,769,994 Hendryx July 8, 1930 2,035,974 McWilliams Mar. 31, 1936 2,353,606 Watts July 11, 1944 

